Taking Costs on Account is advisable, as you don't know which clients won't pay our bills. Clients without assets, new clients to the firm and clients who are based overseas present the highest risk of non-payment and thus the greatest need to pay Costs on Account. Credit control can also present a challenge for small bills which are often not economical to chase, so Costs on Account are highly advisable there too. You should ensure you top up the Costs on Account regularly too. It's a bad client who won't pay Costs on Account when asked. Unfortunately, even clients you have known for years, can become poor payers.